the e-mail was traced back to the computer of paula broadwell. but what agents found instead of a account were salacious e-mails between petraeus and broadwell. >> there had been rumors between him and broadwell for some time. but, frankly, i didn't believe them and neither did just about anybody else i knew. he just didn't seem the type. >> reporter: martha raddatz reports that some of his afghanistan staff worried about how it looked with broadwell spending so much time with him. an official tells abc news that it was just tuesday evening that the head of national intelligence was told. thursday at the white house, petraeus offered his resignation to the president, who waited 24 hours to accept. so shocking because petraeus himself had been critical of officers guilty of infidelity. >> he spoke of them in this tone of contempt that they had exchangesed in this type of behavior. >> this morning, he has no plans to start the investigation. >> david, so many people are questioning the timing of this, coming just days after the election, if the fbi